This invention relates to load testing foundation shafts and more particularly to reaction tie-down systems used to provide reaction to axial test loads applied to foundation shafts.
Foundation shafts are used frequently in the construction of modern buildings to properly support the building foundation on various types of soils. Although the behavior of soils can be predicted to some extent, such behavior is not an exact science and actual tests must be conducted in the field to determine the load-bearing capabilities for a given foundation shaft design located in a particular site. The final number and location of foundation shafts needed to support a particular building can then be estimated from the test results. The test results are necessary not only to ensure an adequate margin of safety, but to inform the building contractor whereby an unnecessary number of foundation shafts are not drilled.
One conventional technique for measuring the load carrying capability of a given foundation shaft is the reaction system whereby an axial load is generated by jacks bearing against load-carrying reaction beams which transmit the load to reaction anchor shafts aligned with the test foundation shaft. In one conventional reaction test system design, a steel adaptor girder is aligned within the anchor shaft after the shaft has been drilled, and the anchor shafts are then filled with suitable reinforcing material and concrete.
The conventional apparatus is, however, time consuming and costly to assembly and use. These adaptor girders must be held in relatively precise vertical alignment while the concrete cures to prevent eccentric loading by the reaction beams. Further, a substantial portion of the girder is required to be imbedded in the concrete to obtain sufficient bond to prevent the girder from pulling loose from the anchor shaft during application of the test load. The final assembly between a girder support system and the adaptor girders has to be performed on-site, and the mating bolt holes custom drilled to precisely align the load-carrying members. If the adaptor girder has not been aligned with sufficient precision in the first instance, it is apparent that no correction can be obtained once the concrete has cured in place. Additionally, at the conclusion of the testing, additional time and labor is required to remove the exposed portion of the adaptor girder and material costs are increased by having to leave the imbedded portion of the adaptor girder in place in the cast concrete anchor shaft.
These disadvantages of the prior art are overcome by the present invention, however, and an improved reaction test system is provided for axially loading foundation shaft members.